1. Field of the Invention
The present invention relates to a universal paper cassette for receiving sheets of paper for a printer, a copier, or the like, and more particularly, to a universal paper cassette in which the pressing force of a paper pressing plate can be controlled.
2. Description of the Related Art
In general, a printing device such as a printer or a copier is provided with a universal paper cassette for receiving sheets of paper and sequentially feeding the received sheets of paper into a main body of the printing device. A cassette constructed to receive a certain size of paper sheets or a universal paper cassette constructed to receive various paper sizes with one case is used as a case for receiving paper.
FIG. 1 is a partially cut away perspective view schematically showing a conventional universal paper cassette.
Referring to FIG. 1, a conventional universal paper cassette is provided with a case 10, a pair of side guide members 14 installed within the case 10 to be slidable widthwise according to the width of received paper sheets for supporting both sides of the received paper sheets, a lengthwise guide member 16 installed within the case 10 to be slidable lengthwise according to the length of the paper sheets for supporting the front ends of the paper sheets, a pair of finger members 17 extending from each side guide member 14 for pressing and supporting both rear corners of the paper sheets, and a paper pressing plate 12 on which the paper sheets are laid. The paper pressing plate 12 is pivotally connected to the sides of the case 10 by pins P. Further, springs 18 which press the paper pressing plate 12 upward are installed under the paper pressing plate 12. In addition, since racks 15 are installed at each of the side guide members 14, and a pinion (not shown) is interposed between the racks 15 and meshes with the racks 15, the sliding movement of the side guide members 14 can be guided.
In order to load paper sheets of a desired size into a conventional universal paper cassette as described above, a user separates the side guide members 14 wide enough to lay the paper sheets on the paper pressing plate 12. At this time, the finger members 17 move together with the respective side guide members 14. After loading the paper sheets, the user adjusts the side guide members 14 in the direction indicated by arrow B to closely contact and support both sides of the paper sheets. Also, while the lengthwise guide member 16 is adjusted in the direction indicated by arrow A to support the front ends of the paper sheets, the front ends of the paper sheets are adjusted to be aligned with the front end of the paper pressing plate 12 and the rear end portions of the paper sheets must be interposed between the paper pressing plate 12 and the finger members 17. The sheets of paper so positioned as described above stay ready for use while being pressed against the finger members 17 by the elastic force of the spring 18 under the paper pressing plate 12. In order to use paper sheets of another size, after a user removes paper sheets having been in use from the case 10 and lays the paper sheets to be used on the paper pressing plate 12, the user adjusts the side guide members 14 and the lengthwise guide member 16 as described above, and thereby the change of paper sheets is completed.
However, the conventional universal paper cassette as described above has a disadvantage in that the objective of the universal paper cassette for using various sizes of paper sheets is not effectively achieved. That is to say, since the elastic force of each spring 18 is constant, an appropriate elastic force cannot be exerted according to variations in the size of paper sheets. In other words, when a larger size paper sheet is used, the weight of the paper sheets increases. Therefore, the elastic forces of the springs 18 exerted on the paper pressing plate 12 is decreased due to the weight of the paper sheets and a pressing force between the finger members 17 and the paper pressing plate 12 is decreased. On the contrary, when a smaller size paper sheet is used, the elastic forces of the springs 18 exerted on the paper pressing plate 12 is increased and a pressing force between the finger members 17 and the paper pressing plate 12 is increased. Therefore, paper jams in which more than two paper sheets are fed at a time may occur in the main body of a printing device.